The numbers of persons who can be enrolled by their iris patterns with no identity collisions is studied in relation to the biometric entropy extracted, and the decision operating threshold. The population size at which identity collision becomes likelier than not, given those variables, defines iris "capacity." The general solution to this combinatorial problem is derived, in analogy with the well-known "birthday problem." Its application to unique biometric identification on national population scales is shown, referencing empirical data from US NIST (National Institute of Standards and Technology) trials involving 1.2 trillion (1.2 x 10^(12) ) iris comparisons. The entropy of a given person's two iris patterns suffices for global identity uniqueness.

翻译：研究了在给定提取的生物特征熵和决策操作阈值条件下，通过虹膜模式进行身份注册且不产生身份碰撞的人数上限。在此类变量下，身份碰撞可能性超过不可能的人口规模定义了虹膜“容量”。通过类比著名的“生日问题”，推导出这一组合问题的通用解。研究展示了该方法在国家级人口规模下实现唯一生物特征识别中的应用，并引用了美国国家标准与技术研究院（NIST）涉及1.2万亿（1.2 x 10^(12)）次虹膜比较的实证数据。结果表明，一个人的两个虹膜模式所蕴含的熵足以实现全球身份唯一性。